Remote radio head unit system with wideband power amplifier and method

ABSTRACT

A remote radio head unit (RRU) system for multiple operating frequency bands, multi-channels, driven by a single or more wide band power amplifiers. More specifically, the present invention enables multiple-bands RRU to use fewer power amplifers in order to reduce size and cost of the multi-band RRU. The present invention is based on the method of using duplexers and/or interference cancellation system technique to increase the isolation between the transmitter signal and receiver signal of the RRU.

RELATED APPLICATIONS

This application claims the benefit of the following applications,attached as Appendices:

U.S. patent application Ser. No. 12/415,676, filed Mar. 31, 2009, andthrough it U.S. Patent Appn Ser. No. 61/041,164, filed Mar. 31, 2008;which also claims the benefit of U.S. Provisional Patent ApplicationSer. No. 61/172,642, filed Apr. 24, 2009;U.S. patent application Ser. No. 12/603,419, filed Oct. 21, 2009, andthrough it U.S. patent application Ser. No. 12/108,507, filed Apr. 23,2008, and through it U.S. Patent Application Ser. No. 60/925,577, filedApr. 23, 2007;U.S. patent application Ser. No. 12/330,451 filed Dec. 8, 2008, andthrough it U.S. Patent Application Ser. No. 61/012,416, filed Dec. 7,2007;U.S. patent application Ser. No. 11/961,969, filed Dec. 20, 2007, andthrough it U.S. Patent Application Ser. No. 60/877,035, filed Dec. 26,2006, and U.S. Patent Application Ser. No. 60/925,603, filed Apr. 23,2007;U.S. patent application Ser. No. 12/108,502, filed Apr. 23, 2008, andthrough it U.S. patent application Ser. No. 12/021,241, filed Jan. 28,2008, and through that to U.S. Patent Application Ser. No. 60/897,746,filed Jan. 26, 2007.U.S. Patent Application Ser. No. 61/288,838, filed Dec. 21, 2009,entitled MULTI-BAND WIDEBAND POWER AMPLIFIER DIGITAL PREDISTORTIONSYSTEM AND METHOD and naming as inventors Wan-Jong Kim, Kyoung-Joon Cho,and Shawn Patrick Stapleton.U.S. Patent Application Ser. No. 61/288,840, filed Dec. 21, 2009,entitled REMOTE RADIO HEAD UNIT SYSTEM WITH WIDEBAND POWER AMPLIFIER ANDMETHOD and naming as inventors Chengxun Wang and Shawn PatrickStapleton.U.S. Patent Application Ser. No. 61/288,844, filed Dec. 21, 2009,entitled MODULATION AGNOSTIC DIGITAL HYBRID MODE POWER AMPLIFIER SYSTEMAND METHOD and naming as inventors Wan-Jong Kim, Kyoung-Joon Cho, ShawnPatrick Stapleton, Ying Xiao.U.S. Patent Application Ser. No. 61/288,847, filed Dec. 21, 2009,entitled HIGH EFFICIENCY, REMOTELY RECONFIGURABLE REMOTE RADIO HEAD UNITSYSTEM AND METHOD FOR WIRELESS COMMUNICATIONS and naming as inventorsWan-Jong Kim, Kyoung-Joon Cho, and Shawn Patrick Stapleton, and YingXiao.All of the foregoing are incorporated herein by reference for allpurposes.

FIELD OF THE INVENTION

The present invention generally relates to wireless communicationsystems using power amplifiers and remote radio head units (RRU or RRH).More specifically, the present invention relates to RRU which are partof a distributed base station in which all radio-related functions arecontained in a small single unit that can be deployed in a locationremote from the main unit.

BACKGROUND OF THE INVENTION

Wireless and mobile network operators face the continuing challenge ofbuilding networks that effectively manage high data-traffic growthrates. Mobility and an increased level of multimedia content for endusers require end-to-end network adaptations that support both newservices and the increased demand for broadband and flat-rate Internetaccess. In addition, network operators must consider the mostcost-effective solutions to expand network capacity and evolutiontowards 4G and beyond.

Wireless and mobile technology standards are evolving towards higherbandwidth requirements for both peak rates and cell throughput growth.Thee latest standards supporting this are HSPA+, WiMAX, TD-SCDMA andLTE. The network upgrades required to deploy networks based on thesestandards must balance the limited availability of new spectrum,leverage existing spectrum, and ensure operation of all desiredstandards. This all must take place at the same time during thetransition phase, which usually spans many years.

Distributed open base station architecture concepts have evolved inparallel with the evolution of the standards to provide a flexible,cheaper, and more scalable modular environment for managing the radioaccess evolution. For example, the Open Base Station ArchitectureInitiative (OBSAI), the Common Public Radio Interface (CPRI), and the IRInterface standards introduced standardized interfaces separating theBase Station server and the remote radio head part of a base station byan optical fiber.

The RRU concept is a fundamental part of a state-of-the-art base stationarchitecture. 2G/3G/4G base stations are typically connected to RRUsover optical fibers. Either CPRI, OBSAI or IR Interfaces may be used tocarry data to the RRH to cover a three-sector cell. The RRU incorporatesa large number of digital interfacing and processing functions.Traditionally, a multi-channel RRU means that multiple antennas areused, typically with two power amplifiers for two distinct bands. Aduplexer is used to combine the two power amplifier outputs. Switchesare used to isolate the transmit signals from the received signals asoccurs in a Time Division Synchronous Code Division Multiple Access(TD-SCDMA) modulation. To extent the prior art architecture to multiplebands (i.e., two or more bands) implementation would consist of addingadditional channelized power amplifiers in parallel. The output of theadditional power amplifiers is typically combined in an N by 1 duplexerand fed to a single antenna.

While conventional RRU architecture offers some benefits, RRUs to dateare power-inefficient, costly and inflexible. Further, their poorDC-to-RF power conversion insures that they will have a large mechanicalhousing. In addition, current RRU designs are inflexible. As standardsevolve, there is a need for multi-band RRUs that can accommodate two ormore operating channels using a single wideband power amplifier. Thiscreates an isolation problem at the individual receivers because thewideband power amplifier is always turned on. Isolation between thewideband transmitter and receivers is a problem with any modulationstandard (HSPA+, WiMAX, LTE, etc.) when multi-band RRUs are developedusing a single power amplifier. This is a common problem for allcommunication systems that utilize a wideband power amplifier in amulti-band scenario.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide a highperformance and cost effective technique for implementing RRU systemsthat service multi-frequency bands. Further, the present disclosureenables a RRU to be field-reconfigurable, and supports multi-modulationschemes (modulation agnostic), multi-carriers, multi-frequency bands,and multi-channels. The present invention also serves multi-frequencybands within a single RRU to economize the cost of radio networkdeployment. In particular, the present invention resolves an isolationissue for a RRU with fewer power amplifiers than the number of operatingfrequency bands. Multi-mode radios capable of operating according toGSM, HSPA, LTE, TD-SCDMA and WiMAX standards and advanced softwareconfigurability are key features in the deployment of more flexible andenergy-efficient radio networks.

The present invention achieves the above objects using techniquesgenerally based on methods and techniques for maximizing the isolationbetween the transmitted signal (Tx Signal) and the received signal (RxSignal). The Tx Signal may comprise noise generated at the output of thepower amplifier or it may comprise an unwanted transmitter band leakinginto the receiver. With the use of the present invention, conventionalRRU's can be extended to a multi-band and multi-channel configuration.Multi-band means that more than one frequency bands are used in the RRUand multi-channel means that more than one output antenna is used.Various embodiments of the invention are disclosed.

An embodiment of the present invention utilizes duplexers, switches andcirculators to maximize the isolation between the transmitter andreceiver. Another embodiment of the present invention utilizes aninterference Cancellation System (ICS) together with duplexers, switchesand circulators.

Applications of the present invention are suitable for use with allwireless base-stations, remote radio heads, distributed base stations,distributed antenna systems, access points, repeaters, mobile equipmentand wireless terminals, portable wireless devices, and other wirelesscommunication systems such as microwave and satellite communications.The present invention is also field upgradable through a link such as anEthernet connection to a remote computing center.

THE FIGURES

Further objects and advantages of the present invention can be morefully understood from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a TD-SCDMA dual-band single PAconfiguration in a remote radio head unit system in accordance with thepresent invention.

FIG. 2 is a block diagram of the TD-SCDMA dual-band single PA with aInterference Cancellation System (ICS) configuration in a remote radiohead unit system in accordance with the present invention.

FIG. 3 is a FDD Modulation Agnostic Dual-Band Remote Radio Head with anInterference Cancellation System.

FIG. 4 is an Interference Cancellation System using Power Detection.

FIG. 5 is a TDD Modulation Agnostic Dual-Band Remote Radio Head with anInterference Cancellation System.

FIG. 6 is an Interference Cancellation System using Correlation.

GLOSSARY OF TERMS

-   ACLR Adjacent Channel Leakage Ratio-   ACPR Adjacent Channel Power Ratio-   ADC Analog to Digital Converter-   AQDM Analog Quadrature Demodulator-   AQM Analog Quadrature Modulator-   AQDMC Analog Quadrature Demodulator Corrector-   AQMC Analog Quadrature Modulator Corrector-   BPF Bandpass Filter-   CDMA Code Division Multiple Access-   CFR Crest Factor Reduction-   DAC Digital to Analog Converter-   DET Detector-   DHMPA Digital Hybrid Mode Power Amplifier-   DDC Digital Down Converter-   DNC Down Converter-   DPA Doherty Power Amplifier-   DQDM Digital Quadrature Demodulator-   DQM Digital Quadrature Modulator-   DSP Digital Signal Processing-   DUC Digital Up Converter-   EER Envelope Elimination and Restoration-   EF Envelope Following-   ET Envelope Tracking-   EVM Error Vector Magnitude-   FFLPA Feedforward Linear Power Amplifier-   FIR Finite Impulse Response-   FPGA Field-Programmable Gate Array-   GSM Global System for Mobile communications-   I-Q In-phase/Quadrature-   IF Intermediate Frequency-   LINC Linear Amplification using Nonlinear Components-   LO Local Oscillator-   LPF Low Pass Filter-   MCPA Multi-Carrier Power Amplifier-   MDS Multi-Directional Search-   OFDM Orthogonal Frequency Division Multiplexing-   PA Power Amplifier-   PAPR Peak-to-Average Power Ratio-   PD Digital Baseband Predistortion-   PLL Phase Locked Loop-   QAM Quadrature Amplitude Modulation-   QPSK Quadrature Phase Shift Keying-   RF Radio Frequency-   RRU Remote Radio Head Unit-   SAW Surface Acoustic Wave Filter-   UMTS Universal Mobile Telecommunications System-   UPC Up Converter-   WCDMA Wideband Code Division Multiple Access-   WLAN Wireless Local Area Network

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a novel RRU system that utilizes a widebandpower amplifier. The present invention is a hybrid system of digital andanalog modules. The interplay of the digital and analog modules of thehybrid system eliminates interference between the wideband poweramplifier output and the receiver's inputs. The present invention,therefore, achieves higher Transmitter (Tx) to Receiver (Rx) isolationwhen using wideband power amplifiers with multiple frequency bands.

Referring first to FIG. 1, an embodiment of some aspects of theinvention is shown in block diagram form. FIG. 1 depicts the analogsection of a dual channel RRU. In this embodiment a single widebandpower amplifier 404 is used. The two distinct frequency band signals arecombined in a duplexer 403 and input to the wideband power amplifier404. The output of the wideband power amplifier 404 is sent to adiplexer 405 in order to separate the two frequency band signals. Thisconfiguration enables the individual transmitter frequency bands to beindependently turned-off. The Tx switches 405 and 407 are placed in thesignal path after the diplexer 405. The signals are then passed throughcirculators 411 and 412 and a duplexer 413 in order to gain furtherisolation between the Tx signals and the Rx signals. The Rx switches 408and 410 are placed on the third port of the circulator. Alternatively,two or more frequency bands can be combined in one power amplifier usingthe same architecture as in FIG. 1.

FIG. 2 illustrates a further alternative embodiment of the dual-bandsingle wideband power amplifier RRU analog section. Although theembodiment in FIG. 2 shows a dual-band implementation, the invention canalso be utilized in single band embodiments. In the embodiment of FIG.2, an interference cancellation system (ICS) 520 is utilized to improvethe isolation between the transmitter and receivers. The interferencecancellation system generates a replica of the unwanted feedback signalbut in anti-phase so as to eliminate the interference. The interferencecancellation system comprises five primary blocks: Delay, variableattenuator, variable phase shifter, Down Converter (DNC) and DSPcontroller, alternative arrangements of which are shown in FIGS. 4 and6, discussed hereinafter. The ICS receives incoming signals throughlinks 506 and 507. The anti-phase output of the ICS is combined with thesignals from switches Rx1 and Rx2, indicated at 510 and 511,respectively, by the use of adders 551 and 552, and the resulting signalprovides the inputs to the LNA's 515 and 516. The ICS is an adaptivecontrol system which continuously adjusts the variable attenuator aswell as the variable phase shifter so as to maintain good interferencecancellation. Alternatively, an embodiment of the ICS can comprise afixed attenuator and phase shifter setting, eliminating the need for DSPcontrol, although in at least some cases this results in inferiorperformance compared to the adaptive ICS system of FIG. 2. The remainingelements of FIG. 2 correspond to those shown in FIG. 1, and areindicated by the same numerals except that the most significant digithas been changed from “4” to “5”.

FIG. 3 shows another embodiment of the analog section of a dual-bandsingle wideband power amplifier RRU in Frequency Division Duplex (FDD)mode. This embodiment is modulation agnostic for FDD standard systems,and elements 601-604 operate analogously to elements 401-404 of FIG. 1.The triplexer 608 separates the transmitter bands from the receiverbands. FDD systems use different transmit and receive frequencies foreach channel. The function of the triplexer 608 is to pass the output ofpower amplifier 604 to the antenna while isolating the receivers fromthe transmitter output. The ICS 609 system is utilized for increasingthe isolation between the transmitter output and the receiver inputs aswith FIG. 2, and receives the output of PA 604 through link 605. Theoutput of the ICS 609 is combined with the appropriate triplexer outputsthrough adders 610 and 611, and the links 605 feeding the LNA's 612 and613.

FIG. 4 is a depiction of one embodiment of an Interference CancellationSystem (ICS). The function of the ICS is to generate a replicate of theinterfering signal and place it in anti-phase to the interference,thereby eliminating the interfering signal. The input to the ICS systemis a sample of the power amplifier output. Coupler 605 is used to samplethe power amplifier output. The power amplifier's output is sampled andsent to a diplexer 710. This separates the two frequencies into distinctsections. The delay block 701 time-aligns the feedback interferingsignal with the sampled power amplifier output. The variable attenuator702 is adjusted to insure that the interfering signal and the sampledsignal have equal magnitude. The variable phase shifter 703 is adjustedto insure that the interfering signal and the sampled signal are inanti-phase. A Digital Signal Processor (DSP) 707 or Microprocessor isused to control the attenuator and phase shifter. A power detectionbased adaptive algorithm in the DSP continuously monitors the signal atthe Down Converter (DNC) 708 output and minimizes the level of theinterference based on the detected power level. The power level of theinterference is measured at the receiver while that band is in thetransmit mode of operation. The second band is similarly processed usingelements 704, 705 and 706.

FIG. 5 shows an embodiment of the analog section of a dual-band singlewideband power amplifier RRU in Time Division Duplex (TDD) mode. Thisembodiment is modulation agnostic for TDD standard systems. The outputof wideband power amplifier 804 feeds a circulator 807. The circulatorprovides some isolation between the transmitted signals and the receiverinputs. A multi-band filter 820 is placed between the circulator and theoutput antenna in order to attenuate out-of-band emissions. The thirdport of the circulator 807 is delivered to a diplexer 808, whichseparates the two distinct operating bands. TDD mode requires thetransmitter and receiver to operate using the same frequency band atdistinct times. In order to provide isolation between the transmitterand receiver, switches 821, 822 are used. The switches can provide someisolation but additional isolation may be required depending on thesystem specifications. The ICS 809 can provide additional isolationbetween the transmitter output and the receiver inputs in the mannerdescribed above.

FIG. 6 is a depiction of another embodiment of an InterferenceCancellation System (ICS). The function of the ICS is to generate areplicate of the interfering signal and place it in anti-phase to theinterference, thereby eliminating the interfering signal. The input tothe ICS system is a simple of the power amplifier output. The poweramplifier's output is sampled and sent to a diplexer 910. This separatesthe two frequencies into distinct sections. The delay block 901 timealigns the feedback interfering signal with the sampled power amplifieroutput. The variable attenuator 902 is adjusted to insure that theinterfering Signal and the sampled signal have equal magnitude. Thevariable phase shifter 903 is adjusted to insure that the interferingsignal and the sampled signal are in anti-phase. A Digital SignalProcessor (DSP) 907 or Microprocessor is used to control the attenuatorand phase shifter. A correlation-based adaptive algorithm in the DSP isused to minimize the level of interference. The DSP correlates the twosignals by controlling the output of switch 911 and the output of switch912 after the signals have been translated to baseband using the twoDownconverters 920 and 909. The switches 911 and 912 alternate betweenthe two channels. The objective of the algorithm is to minimize thecorrelation between the sampled power amplifier output and theinterference at the receiver. The computed correlation coefficient isused as the error function in an adaptive algorithm such as a Least MeanSquared (LMS) algorithm.

From the foregoing teachings, those skilled in the art will appreciatethat the RRU system of the present invention enables the use of singlewideband power amplifier for multi-band operation, which consequentlysaves hardware resources and reduces costs. The RRU system is alsoreconfigurable and field-programmable since the algorithms can beadjusted like software in the digital processor at anytime.

Moreover, the RRU system is agnostic to modulation schemes such as QPSK,QAM, OFDM, etc. in CDMA, TD-SCDMA, GSM, WCDMA, CDMA2000, and wirelessLAN systems. This means that the RRU system is capable of supportingmulti-modulation schemes, multi-frequency bands and multi-channels.

Although the present invention has been described with reference to thepreferred embodiments, it will be understood that the invention is notlimited to the details described thereof. Various substitutions andmodifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

1. (canceled)
 2. An interference mitigation system for improvingisolation between transmitters and receivers in wireless communicationssystems comprising: a transmitter that transmits a transmit signalduring a first time slot while a switch is in a first position; afeedback coupler that generates a feedback signal based on a transmitsignal, wherein a characteristic of the feedback signal isrepresentative of a characteristic of the transmit signal, aninterference cancellation unit that processes the feedback signalgenerate a processed signal; a receiver that receives an intake signalduring a second time slot while the switch is in a second position,wherein the intake signal includes a first component from a signalreceived by a receiver and a second component from interference from thetransmit signal, wherein whether the switch is in the first position orthe second position is based on a time-division multiplexing technique;and a combiner that combines the intake signal received with theprocessed signal to generate a combined signal.
 3. The interferencemitigation system of claim 2, wherein the interference cancellation unitincludes a delay block, an attenuator and a phase shifter.
 4. Theinterference mitigation system of claim 2, further comprising a poweramplifier that amplifies the received intake signal prior to combiningthe intake signal with the processed signal.
 5. The interferencemitigation system of claim 2, further comprising switch-operating logicthat controls the position of the switch.
 6. The interference mitigationsystem of claim 2, wherein the interference cancellation unit processesthe feedback signal and a second feedback signal using a correlationtechnique.
 7. The interference mitigation system of claim 2, wherein theprocessing of the feedback signal includes isolating each of a pluralityof frequency bands within the feedback signal.
 8. The interferencemitigation system of claim 2, further comprising a second switch thatchanges its position at times corresponding to the time-divisionduplexing technique.
 9. The interference mitigation system of claim 2,further comprising a second feedback coupler for generating a secondfeedback signal based on the combined signal, wherein the secondfeedback signal is representative of the combined signal, wherein theinterference cancellation unit further processes the second feedbacksignal to generate the processed signal.
 10. A method for improvingisolation between transmitters and receivers in wireless communicationssystems, the method comprising: transmitting a transmit signal during afirst time slot while a switch is in a first position; generating afeedback signal based on a transmit signal, wherein a characteristic ofthe feedback signal is representative of a characteristic of thetransmit signal; processing the feedback signal generate a processedsignal; receiving an intake signal during a second time slot while theswitch is in a second position, wherein the intake signal includes afirst component from a signal received by a receiver and a secondcomponent from interference from the transmit signal, wherein whetherthe switch is in the first position or the second position is based on atime-division multiplexing technique; and combining the intake signaland the processed signal to generate a combined signal.
 11. The methodof claim 10, wherein the processing includes one or more of introducinga delay, attenuation and phase shift to the feedback signal.
 12. Themethod of claim 10, wherein the processing includes shifting a phase ofthe feedback signal.
 13. The method of claim 10, wherein the processingincludes adjusting a magnitude of the feedback signal based on amagnitude of another signal.
 14. The method of claim 10, wherein thetransmit signal and the intake signal include modulations within a samefrequency band.
 15. The method of claim 10, wherein the feedback signaland a second signal are processed using a correlation technique.
 16. Themethod of claim 10, further comprising causing a position of a secondswitch to change at times corresponding to the time-division duplexingtechnique.
 17. The method of claim 10, wherein the processing of thefeedback signal includes isolating each of a plurality of frequencybands within the feedback signal.
 18. The method of claim 10, furthercomprising generating a second feedback signal based on the combinedsignal, wherein the second feedback signal is representative of thecombined signal, and wherein the feedback signal is processed with thesecond feedback signal to generate the processed signal.